322 PROCEEDINGS OF THE ACADEMY OF [1893. 



are growing at their headwaters. The time of occupancy by these 

 two types of streams has been so short that the interspaces are flat- 

 topped and undrained, and the channels' steep-sided and canon- 

 like. 



(c) Estuarine Condition. — Even in this brief period the streams of 

 the coastal prairie have been subjected to an accident. All the 

 larger streams are at their mouths estuarine. They are also flow- 

 ing, even on the plain many miles from the shore, in channels with 

 little slope. These facts record a slight submergence since the 

 greatest elevation, though the phenomenon is also due in part 

 to the overburdened condition of the streams. 



(d) Young, Growing Coast Line. — The extended rivers helped to 

 form the coastal plain when the shore line was farther inland, and 

 they are now at work with the aid of tides, waves and currents in 

 the construction of a similar plain along its margin. Each large 

 river is overburdened with sediment derived from the Tertiary 

 clays, the Cretaceous, and Palaeozoic rocks, and this sediment is 

 being used by the waves and tides in the construction of land. The 

 coast line is growing outward. Shoals, bars, and islands are regis- 

 ters of this growth, and the beaches, even the much boasted beach 

 at Galveston, upon which the surf rolls laden and muddy with river 

 furnished sediment, show the progress of outward growth. The har- 

 bors of Texas exist because the river mouths are fjorded, and 

 because protective bars and islands have been thrown across the 

 mouths of the estuaries, by the currents laden with sediment brought 

 down by the rivers. They are poor harbors because the excess of 

 sediment thus furnished is being deposited in the estuaries. The 

 engineering improvements proposed for the harbors of the Texas 

 coast must take into account this outward growth of the coast 

 line. 



The bars thrown up along the Gulf coast line have enclosed 

 lagoons, sometimes quite completely, and here is formed one of the 

 few kinds of lacustrine basins in Texas. 



3. — The Rolling Forested Tertiary Area. 



(a) Topographic Description. — This country l9 consists largely of 

 the inshore part of the bottom of the old Tertiary Sea, which once 

 covered the whole Gulf coast. This area has been elevated into a 



1!l The description in this paragraph is abstracted from Penrose's report on the 

 Gulf Tertiary of east Texas. (First Ann. Kept., Texas Geol. Survey, 1889, pp. 

 7-13), the abstracts in most cases being verbatim quotations. 



